The least impressive thing about last night’s sterling Republican foreign-policy debate from venerable Constitution Hall in Washington DC was the overproduced opening, as CNN’s Wolf Blitzer introduced the candidates as if they were contestants on a quiz show instead of auditioning for the White House.

Mercifully, that was the extent of the frivolousness that’s marred too many of the earlier debates. Once past that, we got an articulate, informed and serious group of candidates responding to sober, intelligent questions — most of which were posed from the audience by associates of two conservative think tanks, Heritage Foundation and the American Enterprise Institute.

In the crispest debate since the series back in May, everyone was on his or her game. There were no gaffes, no flubs, no disastrous memory losses. The candidates — almost any one of whom would have a real chance of unseating President Obama in next year’s presidential election — were all smooth and polished, sticking to their well-staked-out issues.

Indeed, they’ve become like characters in a long-running sitcom, with each one slickly playing his or her assigned role.

There’s Ron Paul, the wacky libertarian who believes in a kind of international Golden Rule: do unto other nations as you would have them do unto you. There’s Michele Bachmann, consistently assailing Obama. And Rick Santorum, the bright kid who always complains he’s not getting enough attention from the teacher.

But there was one big difference last night: This was the first debate in which Mitt Romney, the eternal but generally unloved front-runner, was just another figure on stage, looking nervously over his shoulder not just at the man standing next to him, Rick Perry (who had his best debate performance to date) but at the man who’s supplanting him atop the polls, Newt Gingrich.

True, Newt couldn’t score any cheap points by going after the moderator, as “Blitz” (as Herman Cain delightfully called him) kept the tone elevated. But this kind of forum plays to Gingrich’s strengths — a firm grasp of both foreign and domestic issues and how they relate, married to a newfound consistency of purpose that allows him to talk straight and play to the crowd.

For example, Newt got off one of his best lines of the night when he passionately declared that the time had come to take off the gloves with Pakistan by changing the rules of engagement in Afghanistan and allowing US forces to wage war inside the rogue nation under the doctrine of hot pursuit.

He connected again when he argued that if the US were serious about the Middle East, we’d be busily opening up new oil fields and collapsing the price of oil.

Time and again, Gingrich upstaged Romney, not just on the war — Romney’s more conciliatory position on Pakistan was to naively suggest that trade will help the Islamic country move into the 21st century — but on another hot-button issue, immigration.

Somewhat surprisingly, after the beating Perry took on the issue a while back, Newt adopted the “heart position,” arguing that long-rooted families, even if illegal, ought to be given a path to citizenship. “The party that says it’s the party of the family is going to destroy families that have been here for a quarter of a century?” he mused.

That left Romney in the less appealing position of making a dispassionate, utilitarian case for legal immigration — that America needs the talent.

Along with Santorum, Gingrich also endorsed profiling, saying that “you need to use every tool you can possibly use to gather the intelligence,” once again leaving Romney looking like the odd man out.

In short, what we saw last night was a canny veteran outpointing his slicker, younger rival — something no one would’ve believed possible a few months ago when Gingrich’s campaign seemed to collapse, leaving him the butt of jokes about how much he was spending on his third wife’s jewelry.

Will the Gingrich boomlet last? His famous “baggage” would make him an easy target for Obama, but his formidable intellect would counter that in the head-to-head presidential debates. Gingrich now needs to stay on this focused path and not indulge his unfortunate penchant for faddish notions and shooting from the lip.

But last night also helped Mitt. Unlike Bachmann and Cain (who showed once again that he knows absolutely nothing about the world beyond the US), Gingrich can take the nomination away from him. Let’s see if he raises his game now as well.